U.S. patent number 4,807,798 [Application Number 06/935,362] was granted by the patent office on 1989-02-28 for method to produce metal matrix composite articles from lean metastable beta titanium alloys.
This patent grant is currently assigned to The United States of America as represented by the Secretary of the Air. Invention is credited to Daniel Eylon, Francis H. Froes.
United States Patent |
4,807,798 |
Eylon , et al. |
* February 28, 1989 |
Method to produce metal matrix composite articles from lean
metastable beta titanium alloys
Abstract
A method for fabricating an improved titanium alloy composite
consisting of at least one high strength/high stiffness filament or
fiber embedded in an alpha-beta titanium alloy matrix which
comprises the steps of providing a rapidly-solidified foil made of
a lean metastable beta titanium alloy, fabricating a preform
consisting of alternating layers of the rapidly-solidified foil and
the filamentary material, and applying heat and pressure to
consolidate the preform, wherein consolidation is carried out at a
temperature below the beta-transus temperature of the alloy.
Inventors: |
Eylon; Daniel (Dayton, OH),
Froes; Francis H. (Xenia, OH) |
Assignee: |
The United States of America as
represented by the Secretary of the Air (Washington,
DC)
|
[*] Notice: |
The portion of the term of this patent
subsequent to March 29, 2005 has been disclaimed. |
Family
ID: |
25466988 |
Appl.
No.: |
06/935,362 |
Filed: |
November 26, 1986 |
Current U.S.
Class: |
228/190; 164/477;
228/193; 228/262.71 |
Current CPC
Class: |
C22C
47/20 (20130101); C22C 49/11 (20130101) |
Current International
Class: |
C22C
47/00 (20060101); C22C 47/20 (20060101); C22C
49/00 (20060101); C22C 49/11 (20060101); B23K
020/22 (); B23K 031/00 () |
Field of
Search: |
;228/190,193-195,234,263.12,263.21,903,121,178
;428/568,622,623,627,631 ;164/477 |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
|
3991928 |
November 1976 |
Friedrich et al. |
4010884 |
March 1977 |
Rothman |
4406393 |
September 1983 |
Ascani, Jr. et al. |
4411380 |
October 1983 |
McWithey et al. |
4499156 |
February 1985 |
Smith et al. |
|
Other References
Metals Handbook, Ninth Edition, vol. 3, pp. 359, 360, 12/1980.
.
S. J. Savage and F. H. Froes, "Production of Rapidly Solidified
Metals and Alloys", Journal of Metals, vol. 36, No. 4, Apr. 1984,
pp. 20-33..
|
Primary Examiner: Godici; Nicholas P.
Assistant Examiner: Heinrich; Samuel M.
Attorney, Agent or Firm: Bricker; Charles E. Singer; Donald
J.
Government Interests
RIGHTS OF THE GOVERNMENT
The invention described herein may be manufactured and used by or
for the Government of the United States for all governmental
purposes without the payment of any royalty.
Claims
We claim:
1. A method for fabricating a titanium alloy composite consisting
of at least one filamentary material selected from the group
consisting of silicon carbide, silicon carbide-coated boron, boron
carbide-coated boron, and silicon-coated silicon carbide, and a
lean metastable beta titanium alloy which comprises the steps
of:
(a) providing a rapidly solidified foil of said alloy;
(b) fabricating a preform consisting of alternating layers of at
least one of said filamentary materials and said foil; and
(c) applying heat at a level about 1% to 10% below the beta transus
temperature of said alloy and pressure of about 1.5 to 15 ksi for
about 0.25 to 24 hours to consolidate said preform.
2. The method of claim 1 wherein said alloy is Ti-11.5
Mo-6Zr-4.5Sn.
3. The method of claim 1 wherein said alloy is Ti-1OV-2Fe-3Al.
4. The method of claim 1 wherein said alloy is Ti-10Mo.
5. The method of claim 1 wherein said alloy is Ti-6.3Cr.
Description
BACKGROUND OF THE INVENTION
The present invention relates to metal/fiber composite materials,
and in particular, to titanium alloy matrix composites.
Pure titanium is relatively soft, weak and extremely ductile.
Through additions of other elements, the base metal is converted to
an engineering material having unique characteristics, including
high strength and stiffness, corrosion resistance and usable
ductility, coupled with low density.
Titanium is allotropic. Up to 785.degree. C., titanium atoms
arrange themselves in a hexagonal close-packed crystal array called
alpha phase. When titanium is heated above the transition
temperature (beta transus) of 785.degree. C., the atoms rearrange
into a body-centered cubic structure called beta phase. The
addition of other elements to a titanium base will favor one or the
other of the alpha or beta forms.
Titanium alloys are classified into three major groups depending on
the phases present: alpha, beta, or a combination of the two,
alpha-beta. The table below lists common titanium alloy additions.
The elements which favor (stabilize) the alpha phase are termed
alpha stabilizers, those which favor the beta phase are termed beta
stabilizers, and those which do not show a preference for either
phase, but promote one or more desirable properties are termed
neutral. The alpha stabilizers raise the beta transus temperature,
i.e., the temperature at which the atoms rearrange from the alpha
form to the beta form, and beta stabilizers lower the beta transus
temperature.
The so-called beta titanium alloys are, in general, metastable.
That is, within a certain range of beta stabilizer content, the
all-beta matrix can be decomposed by heating the alloy to a
temperature below the beta transus temperature. Such decomposition
can result in allotriomorphic alpha phase or an intimate eutectoid
mixture of alpha and a compound. The beta stabilizers which exhibit
the former type of reaction are called beta isomorphous stabilizers
while those which provide the latter reaction are called beta
eutectoid.
______________________________________ Titanium Alloy Additions
Alpha Beta Stabilizers Stabilizers Isomorphous Eutectoid Neutral
______________________________________ Al Mo Cr Zr O V Mn Sn N Ta
Fe C Nb Si Co Ni Cu H ______________________________________
The metastable beta titanium alloys may be divided into two major
groups, the rich metastable beta alloys and the lean metastable
alloys. Broadly, the division of metastable beta titanium alloys is
made as a result of processing and heat treatment practices: Lean
metastable beta alloys retain the beta phase at room temperature
only after relatively rapid cooling through the beta transus, such
as by water quenching, while rich metastable beta alloys retain the
beta phase at room temperature even after relatively slow cooling,
such as air cooling.
The metastable beta titanium alloys may also be classified as lean
or rich according to their valence electron density (VED). This
value is obtained by multiplying the atomic percent of each element
in the alloy by the number of its valence electrons, i.e., the
number of elecrons available for combining with other atoms to form
molecules or compounds, then dividing the sum of the products by
100. The alloys having a VED equal to or greater than about 4.135
may be classified as rich metastable beta alloys and those with a
VED below about 4.135 may be classified as lean.
Another, perhaps more convenient method for classifying the
metastable beta titanium alloys is to compare the weight percents
of the beta stabilizers. In general, the metastable beta titanium
alloys which contain less than about 14 weight percent total beta
stabilizers may be classified as lean alloys while those which
contain about 14 weight percent or more total beta stabilizers may
be classified as rich.
Examples of metastable beta titanium alloys are given in the
following table:
______________________________________ Total Beta Stabilizers
Composition Class. VED (wt %)
______________________________________ Ti--30Mo Rich 4.352 30
Ti--13V--11Cr--3Al Rich 4.271 24 Ti--3Al--8V--6Cr--4Mo--4Zr Rich
4.176 18 Ti--15V--3Cr--3Al--3Sn Rich 4.144 18 Ti--15V Rich 4.142 15
Ti--11.5Mo--6Zr--4.5Sn Lean 4.129 11.5 Ti--10V--2Fe--3Al Lean 4.108
12 Ti--10Mo Lean 4.105 10 Ti--6.3Cr Lean 4.104 6.3
______________________________________
In recent years, material requirements for advanced aerospace
applications have increased dramatically as performance demands
have escalated. As a result, mechanical properties of monolithic
metallic materials such as titanium often have been insufficient to
meet these demands. Attempts have been made to enhance the
performance of titanium by reinforcement with high strength/high
stiffness filaments.
Titanium matrix composites have for quite some time exhibited
enhanced stiffness properties which approach rule-of-mixtures (ROM)
values. However, with few exceptions, both tensile and fatigue
strengths are well below ROM levels and are generally very
inconsistent.
These titanium composites are fabricated by superplastic
forming/diffusion bonding of a sandwich consisting of alternating
layers of metal and fibers. At least four high strength/high
stiffness filaments or fibers for reinforcing titanium alloys are
commercially available: silicon carbide, silicon carbide-coated
boron, boron carbide-coated boron and silicon-coated silicon
carbide. Under superplastic conditions, the titanium matrix
material can be made to flow without fracture occurring, thus
providing intimate contact between layers of the matrix material
and the fiber. The thus-contacting layers of matrix material bond
together by a phenomenon known as diffusion bonding. At the same
time a reaction ocurs at the fiber-matrix interfaces, giving rise
to what is called a reaction zone. The compounds formed in the
reaction zone may include TiSi, Ti.sub.5 Si, TiC, TiB and
TiB.sub.2. The thickness of the reaction zone increases with
increasing time and with increasing temperature of bonding.
Titanium matrix composites have not reached their full potential,
at least in part because of problems associated with instabilities
of the fiber-matrix interface. The reaction zone surrounding a
filament introduces new sites for crack initiation and propagation
within the composite, which operates in addition to existing sites
introduced by the original distribution of defects in the
filaments. It is well established that mechanical properties are
influenced by the reaction zone, that, in general, these properties
are degraded in proportion to the thickness of the reaction
zone.
The lean metastable beta titanium alloys need to be solution
treated below the beta transus temperature for good combination of
strength and ductility. Due to the coarse grain size in foil
produced by current rolled foil methods, a relatively high
temperature is required for compacting rolled foil (typically above
the beta transus temperature), which leads to further beta grain
coarsening, which in turn degrades both compactability and post
compaction matrix properties.
It is, therefore, an object of the present invention to provide
improved titanium composites.
It is another object of this invention to provide an improved
method for fabricating titanium composites.
Other objects, aspects and advantages of the present invention will
be apparent to those skilled in the art from a reading of the
following description of the invention and the appended claims.
SUMMARY OF THE INVENTION
In accordance with the present invention there is provided an
improved titanium composite consisting of at least one filamentary
material selected from the group consisting of silicon carbide,
silicon carbide-coated boron, boron carbide-coated boron and
silicon-coated silicon carbide, embedded in a lean metastable beta
titanium alloy matrix.
The method of this invention comprises the steps of providing a
rapidly-solidified foil made of a lean metastable beta titanium
alloy, fabricating a preform consisting of alternating layers of
the rapidly-solidified foil and at least one of the aforementioned
filamentary materials, and applying heat and pressure to
consolidate the preform, wherein consolidation is carried out at a
temperature below the beta-transus temperature of the alloy,
thereby reducing the amount of reaction zone between the fiber and
the alloy matrix.
BRIEF DESCRIPTION OF THE DRAWING
In the drawing,
FIG. 1 is a 500x photomicrograph illustrating a portion of a
SCS-6/Beta III composite structure;
FIG. 2 is a 1000x photomicrograph of the fiber/metal interface of
the composite of FIG. 1; and
FIG. 3 is a 1000x photomicrograph showing the interface between
Borsic fiber and rapidly solidified Beta III foil.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The titanium alloys employed according to the present invention are
lean metastable beta titanium alloys. Suitable lean beta alloys
include Ti-11.5Mo-6Zr-4.5Sn (Beta III), Ti-3.5Fe, Ti-1OV-2Fe-3Al,
Ti-10Mo and Ti-6.3Cr.
Several techniques are known for producing rapidly-solidified foil,
including those known in the art as Chill Block Melt Spinning
(CMBS), Planar Flow Casting (PFC), melt drag (MD), Crucible Melt
Extraction (CME), Melt Overflow (MO) and Pendant Drop Melt
Extraction (PDME). Typically, these techniques employ a cooling
rate of about 10.sup.5 to 10.sup.7 deg-K/sec and produce a material
about 10 to 100 microns thick, with an average beta grain size of
about 2 to 20 microns, which is substantially smaller than the beta
grain size in materials produced by ingot metallurgy methods.
The high strength/high stiffness filaments or fibers employed
according to the present invention are produced by vapor deposition
of boron or silicon carbide to a desired thickness onto a suitable
substrate, such as carbon monofilament or very fine tungsten wire.
This reinforcing filament may be further coated with boron carbide,
silicon carbide or silicon. To reiterate, at least four high
strength/high stiffness filaments or fibers are commercially
available: silicon carbide, silicon carbide-coated boron, boron
carbide-coated boron, and silicon-coated silicon carbide.
For ease of handling it is desirable to introduce the filamentary
material into the composite in the form of a sheet. Such a sheet
may be fabricated by laying out a plurality of filaments in
parallel relation upon a suitable surface and wetting the filaments
with a fugitive thermoplastic binder, such as polystyrene. After
the binder has solidified, the filamentary material can be handled
as one would handle any sheet-like material.
The composite preform may be fabricated in any manner known in the
art. For example, alternating plies of alloy foil and filamentary
material may be stacked by hand in alternating fashion. The
quantity of filamentary material included in the preform should be
sufficient to provide about 25 to 45, preferably about 35 volume
percent of fibers.
Consolidation of the filament/sheetstock preform is accomplished by
application of heat and pressure over a period of time during which
the matrix material is superplastically formed around the filaments
to completely embed the filaments. Prior to consolidation, the
fugitive binder, if used, must be removed without pyrolysis
occurring. By utilizing a press equipped with heatable platens and
a vacuum chamber surrounding at least the platens and press ram(s),
removal of the binder and consolidation may be accomplished without
having to relocate the preform from one piece of equipment to
another.
The preform is placed in the press between the heatable platens and
the vacuum chamber is evacuated. Heat is then applied gradually to
cleanly off-gas the fugitive binder without pyrolysis occurring, if
a fugitive binder is used. After consolidation temperature is
reached, pressure is applied to achieve consolidation.
Consolidation is carried out at a temperature in the approximate
range of 10.degree. to 100.degree. C. (18.degree. to 180.degree.
F.) below the beta-transus temperature of the titanium alloy. For
example, the consolidation of a composite comprising Beta III
alloy, which has a beta transus of about 745.degree. C.
(1375.degree. F.), is preferably carried out at about 730.degree.
C. (1350.degree. F.). The pressure required for consolidation of
the composite ranges from about 10 to about 100 MPa (about 1.5 to
15 Ksi) and the time for consolidation ranges from about 15 minutes
to 24 hours or more. Consolidation under these conditions permits
retention of the fine grain size of the alloy matrix.
The following example illustrates the invention:
EXAMPLE
A composite preform was prepared as follows:
Beta III ribbons produced by the pendant drop melt extraction
(PDME) process, having a width of 2 mm., an average thickness of 63
microns and an average beta grain size of 5 microns, were cut into
segments of about 1 inch length. A layer of such segments was
placed into a carburized steel cup lined with CP titanium foil.
SCS-6 fibers were placed on top of the ribbon segments. Another
layer of the ribbon segments was placed over the fibers. Finally, a
CP titanium foil cover was placed over the preform. A plug of
carburized steel was fitted into the cup and the entire assembly
was fitted into a die for hot pressing.
The preform was compacted at 750.degree. C. (1350.degree. F.) at 10
Ksi for 24 hours. The resulting composite is shown in FIG. 1 which
illustrates complete bonding between the SCS-6 fiber and the Beta
III ribbon. The fine grain structure of the rapidly solidified
ribbon (average grain size 5 microns) may also be seen. FIG. 2
illustrates the fiber/alloy interface of this composite at higher
magnification. No reaction zone is visible at the higher
magnification.
FIG. 3 illustrates the interface between Beta III and Borsic fiber
of a composite prepared using rapidly solidified Beta III ribbon
and consolidated as described above. As before, no reaction zone is
visible.
In contrast, a composite prepared using rolled Beta III foil and
SCS-6 fiber, and consolidated at 925.degree. C. (1700.degree. F.)/8
Ksi/2 hr had a reaction zone about 1 micron wide.
Various modifications may be made in the present invention without
departing from the spirit of the invention or the scope of the
appended claims.
* * * * *